Insulation materials are known which comprise a clean, non-toxic, heat barrier made of aluminum foil bonded to polymeric materials.
Examples of such insulation materials, includes aluminum fail backing with foam materials selected from closed cell foams, polyethylene foams, polypropylene foams and expanded polystyrene foams (EPS).
Alternative insulation materials in commercial use are made from aluminum foil bonded to a single or double layer of polyethylene-formed bubbles spaced one bubble from another bubble in the so-called “bubble-pack” arrangement. Such non-foil bubble-packs are used extensively as packaging material, whereas the metal foil bubble-pack is used as thermal insulation in wood frame structures, walls, attics, crawl spaces, basements and the like and as wrapping for hot water heaters, hot and cold water pipes, air ducts and the like. The reflective surface of the metal, particularly, aluminum foil enhances the thermal insulation of the air-containing bubble pack.
Organic polymers, such as polyethylene, are generally considered to be high-heat-release materials. They can easily initiate or propagate fires because, on exposure to heat, they undergo thermal degradation to volatile combustible products. If the concentration of the degradation products in the air is within flammability limits, they can ignite either spontaneously, if their temperature is large enough, or by the effect of an ignition source such as a spark or flame. The ignition of polyethylene can be delayed and/or the rate of its combustion decreased by means of fire retardant materials.
The ultimate aim of fire retardants is to reduce the heat transferred to the polymer below its limit for self-sustained combustion or below the critical level for flame stability. This can be achieved by decreasing the rate of chemical and/or physical processes taking place in one or more of the steps of the burning process. One or a combination of the following can achieve fire extinguishing:
1. creation of a heat sink by using a compound that decomposes in a highly endothermic reaction giving non-combustible volatile products, which perform a blanketing action in the flame, e.g., aluminum or magnesium hydroxide;
2. enhancements of loss of heat and material from the surface of the burning polymer by melt dripping, e.g., mixture of halogenated compounds with free radical initiators;
3. flame poisoning by evolution of chemical species that scavenge H and OH radicals which are the most active in propagating thermo-oxidation in the flame, e.g., hydrogen halides, metal halides, phosphorus-containing moieties;
4. limitation of heat and mass transfer across the phase boundary, between thermal oxidation and thermal degradation by creation of an insulating charred layer on the surface of the burning polymer, e.g., intumescent chart; or
5. modification of the rate of thermal volatilization of the polymer to decrease the flammability of the volatile products; which approach strongly depends, on the chemical nature of the polymer.
Fire retardant materials are generally introduced to the polyethylene as merely additives or as chemicals that will permanently modify its molecular structure. The additive approach is more commonly used because it is more flexible and of general application.
Generally, low density polyethylene films of 1-12 mil, optionally, with various amounts of linear low density polyethylene in admixture when additional strength is required, are used for the above applications. The insulating properties of the bubble pack primarily arise from the air in the voids. Typically, bubble diameters of 1.25 cm, 0.60 cm and 0.45 cm are present.
Regardless of the application method of fire retardant material(s), a satisfactory insulative assembly must have a fire rating of Class A with a flame spread index lower than 16, and a smoke development number smaller than 23. Further, the bonding of the organic polymer films and their aging characteristics must meet the aforesaid acceptable standards. Yet further, the fabrication method(s) of a new fire retardant system or assembly should be similar to the existing technology with reasonable and cost effective modifications to the existing fabrication system/technology. Still yet further, other physical properties of an improved fire standard system must at least meet, for example, the standard mechanical properties for duct materials as seen by existing competitive products.
Fire retardant polyethylene films, wires and cables containing a fire retardant material in admixture with the polyethylene per se are known which generally satisfy cost criteria and certain fire retardant technical standards to be commercially acceptable.
Conventional fire retardant additives are usually compounds of small molecular weights containing phosphorus, antimony, or halogens. The most effective commercially available fire retardant systems are based on halogen-containing compounds. However, due to concerns over the environmental effects of such halogenated compounds, there is an international demand to control the use of such halogenated additives.
Some of the most common halogenated agents are methyl bromide, methyl iodide, bromochlorodifluoromethane, dibromotetrafluoroethane, dibromodifluoromethane and carbon tetrachloride. These halogenated fire retarding materials are usually available commercially in the form of gases or liquids. Unlike chlorine and bromine, fluorine reduces the toxicity of the material and imparts stability to the compound. However, chlorine and bromine have a higher degree of fire extinguishing effectiveness and, accordingly, a combination of fluorine and either chlorine or bromine is usually chosen to obtain an effective fire-retarding compounds.
Other commercially available fire retardant materials that do not include halogens include boric acid and borate based compounds, monoammonium phosphonate, and urea-potassium bicarbonate.
Intumescent compounds which limit the heat and mass transfer by creating an insulating charred layer on the surface of the burning polymer are also considered fire retardant materials. A typical intumescent additive is a mixture of ammonium polyphosphate and pentaerythritol.
Fire retardant additives are often used with organic polymer/resins. Typically, a brominated or chlorinated organic compound is added to the polymer in admixture with a metal oxide such as antimony oxide. Halogenated compounds are also sometimes introduced into the polymer chain by co-polymerization. Low levels i.e. less than 1% W/W are recommended to make adverse effects of halogen-based systems negligible. Another common fire retardant additive is diglycidyl ether of bisphenol-A with MoO3. Other additives to improve the fire retarding properties of polyethylene include, for example, beta-cyclodextrin, magnesium hydroxide and alumina trihydrate, tin oxide, zinc hydroxystannate, and chlorosulphonated polyethylene.
U.S. Pat. No. 6,322,873, issued Nov. 27, 2001 to Orologio, Furio, describes a thermally insulating bubble pack for use in framed structures, walls, crawl spaces and the like; or wrapping for cold water heaters, pipes and the like wherein the bubbles contain a fire retardant material. The improved bubble pack comprises a first film having a plurality of portions wherein each of the portions defines a cavity; a second film in sealed engagement with the first film to provide a plurality of closed cavities; the improvement comprising wherein the cavities contain a fluid or solid material. The flame retardant-containing bubble pack provides improved fire ratings, flame spread indices and smoke development numbers. The preferred embodiments include a layer of metal or metallized film adjacent at least one of the films. However, the efficacious manufacture of the fire retardant-filled bubbles still represents a challenge.
Aforesaid bubble-packs not containing fire retardant materials and having a metallized film layer are known and used for external insulation around large self-standing structures, such as tanks, silos and the like, particularly in the oil and chemical industries, which insulation assembly does not have to meet the rigorous fire retardant standards for insulation in framed structures of residential, commercial and industrial buildings, crawl spaces and the like or wrappings for cold water heaters, pipes and the like, therein.
Metallized films and their methods of production are well-known in the art. One technique is to evaporate an extremely thin layer of nearly pure aluminum onto a surface of the non-porous plastics material under vacuum by a so-called ‘vacuum metallizer’. Preferred metallized films of use in the practise of the invention are metallized aluminum coated polymer films, for example, metallized nylon, metallized polypropylene and metallized polyester, preferably, for example, 48 gauge PET (polyethylene terephthalate).
There is, however, always the need for an insulation assembly, having improved fire retardant standards, particularly when safety building codes are being continually improved.
Standards for many products are generally being raised to enhance safety. This is true for reflective insulation materials for use in buildings, which must meet minimum surface burning characteristics to satisfy codes, such as CAN/ULC S201, UL723, ANSI No. 2.5, NFPA No. 255 and 286, UBC 42-1, ASTM E84-05 and others. These tests cover two main parameters, mainly, Flame Spread and Smoke Developed Values.
Such reflective insulation materials are classified as meeting the ratings as follows:—
Interior Walland Ceiling FinishFlame Speed ValueSmoke Developed ValueClass A 0-250-450Class B26-750-450Class C76-2000-450
The classification determines the environmental allowability of the reflective materials insulation. In this specification, Class A also means Class 1.
The standard ASTM E84 and its variations tests, to date, have included, typically, the use of a hexagonal 50 mm steel wire mesh with 6 mm diameter steel rods spaced at 610 mm intervals to support the insulation materials.
Without being bound by theory, the skilled persons in the art have discovered that the aforesaid use of the wire mesh support in the tests has enabled some reflective insulation materials to satisfy the Class A standard, whereas removal of the support in the test has caused these materials not to meet the standard.
Surprisingly, I have discovered that substitution of metallic foil, particularly, aluminum foil, with a metallized, particularly, aluminum, coating on an organic polymer layer, e.g. polyethylene and more particularly PET (polyethylene teraphthate), favourably enhances the surface burning characteristics of the reflective insulation in the aforesaid ASTM E34 test in the absence of the wire mesh support. The reason for this discovery is not, as yet, understood.
Further, I have discovered that the presence of a fire retardant compound in or on one or more of the polymer layers of a reflective insulation assembly further favourably enhances the surface burning characteristics of the insulation, and in preferred embodiments significantly enhances the safety of the assemblies as to satisfy the criteria set in the most stringent “Full Room Burn Test for Evaluating Contribution of Wall and Ceiling Finishes to Room Fire Growth—NFPA 286.
Metallized polymeric films having an outer lacquer coating are known in the foodstuff packaging industry in order to provide physical protection to the ink printed on the outer metallic surface. Manual contact with the unprotected inked material surface would cause inconvenience to the person and possibly contamination of the foodstuffs, such as confectionary and potato chips when handled by the person. The lacquer-coated outer metallic surface overcomes this problem in the foodstuff art.
Surprisingly, I have found that the most preferred metallized polymeric film reflective insulation materials, particularly the fire-retardant containing assemblies, according to the invention provide improved safety towards fire and also acceptable reflectance and anti-corrosive properties.